It depends on what you are sending - something like Hushmail is good for most purposes (for example, letters to friends), but if you are sending something more serious you might want to do a web search for Anonymous Remailers. There are a few drawbacks to anonymous remailers - 1) they don't always work (test them first) 2) you can only send mail with them, and can't receive anything back.

Also you might want to go through a proxy server to make your connection seem like it is coming from somewhere else. You can do web searches for terms like "open proxy servers" or "proxy server list" to find out where they are and how to use them.

The only truly safe way to send email is using public internet access like a cafe or library from a fake account. In my opinion you can't trust overseas accounts either. The people who pretend to offer anonymous email often change their mind when handed a warrant.

The American FBI has a center in Clarksburgh, West Virginia that actually claims to be able to intercept email from anyone to anyone and trace it back to the orginiating IP. So I would be very, very, careful.

When I'm sending information around, I'll first upload files from my Laptop to Yahoo Briefcase, and then download them later to a PC in an Internet cafe. Next, I use ziplip.com, uboot.com or caramail.com to send the files.

The library/internet cafê idea is good, but be ware; people have been apprehended as a result of video-surveillance alone.

As for proxies; not all open proxies renders the client anonymous. Many proxies reveal originating IP through http_x_forwarded_for_ip.

I would log on with a modem, use several proxy-layers and send the e-mail through an anonymoys e-mail service of choice. For further security I would delete all internet logs and cookies on my computer using a decent disk/file eraser.

I must add that you can write your own e-mailing script in PHP or Perl and upload it to a vulnerable host (faulty upload scripts waiting to be exploited are plentiful). Since you have written the script yourself you can be sure that the e-mail header and source will contrain zero information about you or your connection, and as far as everybody else is concerned the e-mail originated from the host server (as it truly did).